带自由表面后向台阶流的数值模拟研究

Numerical simulation study on backward-facing step flow with free surface

后向台阶流是工程领域中一类常见的流动现象,也是流体力学中复杂剪切流动的一个典型例子。针对自由表面对后向台阶流场的影响,在总结前人研究成果的基础上,本文利用VOF方法追踪自由表面,采用realizable k-ε紊流模型封闭控制方程,建立立面二维数值模型,对带自由表面后向台阶流进行了模拟研究。模拟得到4种特征雷诺数工况下,台阶后纵向流速、紊动能、耗散率、边界压力值和水面流速的沿程分布。模拟结果与原型实验观测结果吻合较好。根据模拟结果,对台阶后流场随特征雷诺数变化的规律以及自由水面对台阶后流场分布、漩涡结构和压力值的影响进行了分析讨论。

The backward-facing step flow is widely encountered in engineering fields,and is also a representative example of complex shear flows.Aiming at the influence from free surface on the backward-facing step flow field,a vertica l2-D numerical model is established herein for making a simulative study on the backward-facing step flow with free surface through tracking free surface with VOF method and closing the governing equations with the k-εturbulence model on the basis of the results of the predecessor’s researches.From the simulation,the streamwise distributions of the longitudinal flow velocities,turbulent kinetic energies,dissipation rates,boundary pressure values and surface flow velocities behind the step under the conditions of four characteristic Reynolds numbers are obtained.The simulation results are better coincided with the observed data from the relevant prototype experiments.In accordance with the simulation results,the law of the change of the backward-facing step flow field along with characteristic Reynolds number as well as the influence from free-water surface on the distribution of the backward-facing step flow field,eddy structure and pressure value are analyzed and discussed as well.